Hot vapor fixing of fusible powder images with azeotropic mixtures



y 1968 YUASH PETE JACOB ETAL 3,383,775

HOT VAPOR FIXING OF FUSIBLE POWDER IMAGES WITH AZEOTROPIC MIXTURES Filed Nov. 25, 1966 YUASH PETE JACOB RONALD L. MILLAR BY 6D ho ATT'Y.

United States Patent 3,383,775 HOT VAPOR FIXING OF FUSIBLE POWDER IMAGES WITH AZEOTROPIC MIXTURES Yuash Pete Jacob, Palos Heights, and Ronald L. Millar, Elmhurst, Ill., assignors to Continental Can Company, New York, N.Y., a corporation of New York Filed Nov. 25, 1966, Ser. No. 597,112

13 Claims. (Cl. 34-23) ABSTRACT OF THE DISCLOSURE Electrostaiically produced power images are fixed in a vapor atmosphere of an azeotropic mixture formed from a two phase mixture of water and a substantially water insoluble solvent.

This invention relates to image fixing methods and more particularly to a method for effecting vapor fixing of electrostatically produced powder images.

In certain electrostatic printing processes, an image is developed by electrostatically depositing a powder on a surface to produce a powder image. The powder image is then affixed to the surface upon which it has been deposited or on another surface to which it has been transferred. One method of fixing powder images is by condensing a liquid solvent onto the image surface'from a heated solvent vapor as described in U.S. Patent 2,624,- 652. In this method, a web of material supporting a powder image is introduced into the atmosphere of vapor of a solvent for the powder. The powder image is rendered a tacky cohesive mass while the presence of the atmosphere of the solvent vapor and while still tacky is removed to ambient air for evaporation of the solvent, leaving the image bonded to the support member.

This above described process is referred to in the art as vapor fixing. It is recognized in the art that there is room for improvement in the vapor fixing step wherein the electrostatic latent image is transformed into a visible image. For example, when a toner containing a black pigment is.vapor fixed, the resultant print generally has a yellowish appearance due to bleeding of the toner, which has an undesirable effect on the resolution of the image.

Now in accordance with the present invention, a method is provided for substantially improved fixing of the electrostatic image whereby yellowing or bleeding of the toner is essentialiy eliminated and the image reproduced with improved resolution and generally finer quality which comprises introducing the electrostatically produced powder image into an atmosphere of an azeotropic solvent vapor which is formed from a two phase mixture of water and a solvent substantially insoluble in water, said azeotrope having a boiling point lower than either component of the azeotropic mixture whereby the vapor concentration is maintained at an amount sufiicient to effect absorption of the vaporized azeotropic solvent by the powdered image and consequent fixing of the image.

The process of the present invention provides intense dark or black reproduction of pictures, and sharp, clear and detailed images using conventional toner powder.

Azeotropic mixture, as the term is used herein, is meant to be a liquid solvent which forms a constant boiling mixture with one or more components.

A specific embodiment of the invention is disclosed in the accompanying drawing which constitutes a schematic representation of an apparatus which may be used for applying the vapors of the azeotropic m xture to a web supporting an electrostatically produced powder image in accordance with the process of the present invention. The apparatus illustrated in the drawing consists of a vapor tank having closed bottom and sides and heated 3,383,775 Patented May 21, 1968 at the bottom by a suitable heating element 11. Heating element 11 may be a heating plate, steam pipes or electrically resistant element. A layer of liquid solvent designated by the numeral 12 is placed in the'bottom of the tank 10. The liquid solvent is a mixture of water and an organic solvent which will form a constant boiling azeotrope with water. A coil 13 carrying water or cooling fluid is located concentrically inside the tank 10 at the top. The azeotropic solvent 12, heated by heating element 11, forms a heavy vapor layer 14 above the liquid 12. Web guide roll 16 and take-up roll 17 are mounted above the tank 10 and a large roller or drum 18 is located inside the vapor zone of the tank. A web supporting an electrostatically produced image is fed through the tank by passing it over roll 16 through the rings of the coil 13 into the vapor zone 14 around drum 18.: and over roller 17. The stirrer 22 is employed to continually mix the reservoir of the two-phase azeotropic mixture 12 contained in the bottom of the tank 10.

In operation, web 20 carrying an unfixed powder image 21 from a powder printing or copying machine (not shown) is drawn through the tank 10 in the path illustrated in the drawing. The powder image is located on the upper or outside face of the web 20 as it passes over roller 16 so as to avoid contact with the roller 17 and affect maximum exposure of the powder image to the vaporized solvent. As the web enters the vapor space 14, the powder image absorbs the azeotropic solvent vapor and becomes adhesive. The temperatureof the vapor is generally at the azeotropic boiling point of the liquid mixture. When the web 20 is passed again through the cooled coil and over take-up roll 17, the vapor is immediately condensed on the coils 13 and any excess solvent is allowed to drain back into the tank 10. As soon as the web is removed from the vapor chamber, the solvent begins to evaporate from the image and the image solidifies and becomes permanently bonded or fixed onto the web material in a fraction of a second. A concentrated vapor a!rnosphere is assured by providing the reservoir of liquid solvent 12 in contact with the vapor phase.

The image powder should be composed of materials which contain a binder which is soluble in solvent contained in the azeotropic vapor atmosphere. The various image materials which have been tried are the usual and commercially available toner materials. Such toners, for example, are available under trademark Xerox Copier Toner and are sold by the Xerox Corporation, Rochester, NY. Xerox 914 Toner, for example, consists of carbon black dispersed in a mixed poly(butylmethacrylate)polystyrene hinder, the carbon black having an average particle size of 850 to 1200 A. Other materials from which fusible powder images may be formed include dyed or pigmented phenol formaldehyde resins, rosin modified phenol formaldehyde, and maleic glycerol resins, polystyrene and butadienestyrene copolymers, asphalts, chlorinated rubber, glycol and glycerol esters of hydrogenated rosin, polyamides, ethyl cellulose, polyvinyl butyral, copolymerized vinyl chloride and vinyl acetate resins, other vinyl resins, alkyd resins, acrylic resins and the like.

It is apparent that a wide variety of powder images can be fixed by use of the process of the present invention, it being only necessary to use an azeotropic mixture of water and a water insoluble solvent which dissolves or renders adhesive the particular binder material of which the image power is composed. Azeotropic mixtures which are useful in the vapor fixing process of the present invention include mixtures of water and water insoluble solvents such as halogenated hydrocarbons such as trichloroethylene, chloroform, carbon tetrachloride and other chlorinated solvents, various freons, aromatic hydrocarbons such as benzene, toluene, xylene, ethyl benzerie, and water immiscible esters such as ethyl acetate and butyl acetate and mixtures thereof. It should be pointed out that the particular solvent/water azeotropic mixture employed depends upon the nature of the particular image powder material and/ or the web upon which the image is to be supported. In all cases, the particular solvent is appropriately selected for the particular combination of material compositions employed.

To illustrate the manner in which the invention may be carried out, the following examples are given. It is to be understood, however, that the examples are for the purpose of illustration and the invention is not to be regarded as limited to any of the specific materials or conditions recited therein.

EXAMPLE I Using an apparatus similar to that illustrated in the drawing, a paper web carrying an unfixed powder image electrostatically printed thereon was exposed to the hot vapors of an azeotropic mixture of trichloroethylene and water heated to the boiling point of the mixture. This azeotropic mixture had a constant boiling point of 73.1 C. (at standard atmospheric pressure) and a vapor composition of 6.8% water and 93.2% trichloroethylene by weight. The powder image was formed with Xerox 914 Copier Toner having an average particle size of 17 microns. The composition of this toner is approximately by weight carbon black, by weight poly(butylmethacrylate) resin, and 65% by weight polystyrene resin.

The unfixed halftone powder image was brought into contact with the hot saturated vapors of the azeotropic mixtures for less than 0.5 second to fuse the particles to the paper web.

For the purpose of comparison, the procedure of Example I was repeated with the exception that the paper web carrying the unfixed powder image was exposed to the boiling vapors of trichloroethylene (boiling point 87.2 C.) alone.

A comparison of the prints fixed by exposing the powder image to the trichloroethylene/water azeotropic mixture vapors with the prints fixed by exposing the powder image to the vapors of trichloroethylene alone indicated that the prints fixed by the trichloroethylene/water azeotrope were cleaner and showed greater contrast and less yellowing than the prints vapor fixed in trichloroethylene alone.

EXAMPLE II The procedure of Example I was repeated using the boiling vapors of the trichloroethylene/water azeotrope to vapor fix a powder image, composed of toners having the following compositions: 90 parts polystyrene, 10 parts carbon black; 65 parts polystyrene, 25 parts isobutyl methacrylate, 10 parts carbon black; 60 parts of a polyamide resin, 40 parts carbon black; 95 parts of a rosin modified phenol formaldehyde resin, 5 parts carbon black.

With each toner composition, comparative runs were made using the vapors of trichloroethylene alone to vapor fix the powder image.

Examination of the fixed prints of these toners indicated that in each case, the prints fixed in the vapors of the trichloroethylene/water azeotropic mixture were superior in quality to those fixed in the vapors of trichloroethylene alone. The halftone prints fixed in the vapors of the azeotropic mixture were clearer with less distortion of print details and had better half tone fidelity than the prints fixed in the vapors of the trichloroethylene alone. Also, the prints fixed in vapors of the azeotropic mixture had less yellowing than prints fixed in the vapors of trichloroethylene alone.

EXAMPLE III The procedure of Example I was repeated with the exception that the powder image was fixed in the boiling vapors of an azeotropic mixture comprised of 85.7% perchloroethylene (B.P. 122 C.) and 14.3% water; the azeotrope having a boiling point of 365 C- For purposes of comparison, the procedure of Example I was repeated with the exception that perchloroethylene alone was used as the vapor fixing agent.

The prints fixed by the vapors of the azeotropic mixture when compared with the prints fixed by the vapors of perchloroethylene alone indicated that the azeotropefixed prints had less yellowing than the perchloroethylene fixed prints.

The prints fixed by the perchloroethylene/ water azeotropic mixture vapors were further compared with prints fixed by trichloroethylene alone. Examination of the prints revealed that the perchloroethylene/water azeotropic mixture produced less yellowing than the trichloroethylene alone, although the boiling points of the two vapors are approximately the same (i.e., 86.5 C. versus 872 C.) indicating that the inclusion of water in the vapor fixing solvent minimizes yellowing of the fixed prints causing an improvement in print quality.

EXAMPLE IV The procedure of Example I was repeated with the exception that the powder image was fixed in the boiling vapors of an azeotropic mixture comprised of 91.1% benzene and 8.9% water; the azeotrope having a boiling point of 69.4 C. at 760 mm.

For purposes of comparison, the procedure of Example I was repeated with the exception that benzene alone was used as the vapor fixing agent.

The prints fixed by the vapors of the azeotropic mixture when compared with the prints fixed by the vapors of benzene alone indicated that the azeotrope-fixed prints had less yellowing than the benzene fixed prints.

EXAMPLE V The procedure of Example I was repeated with the ex ception that the powder image was fixed in the boiling vapors of an azeotropic mixture comprised of 79.8% toluene and 20.2% water, the azeotrope having a boiling point of C. at 760 mm.

For purposes of comparison, the procedure of Example I Was repeated with the exception that toluene alone was used as the vapor fixing agent.

The prints fixed by the vapors of the azeotropic mixture when compared with the prints fixed by the vapors of toluene alone indicated that the azeotrope-fixed prints had less yellowing than the toluene fixed prints.

EXAMPLE VI The procedure of Example I was repeated with the exception that the boiling vapors of an azeotropic mixture comprised of 91.8% by weight ethylacetate and 8.2% by weight water; the azeotrope having a boiling point of 70.4 C. at 760 mm. was used to vapor fix a powder image composed of a toner having the following composition: parts of a rosin modified phenol formaldehyde resin and 5 parts carbon black.

For purposes of comparison, this example was repeated with the exception that ethylacetate alone was used as the vapor fixing agent.

The prints fixed by the vapors of the azeotropic mixture when compared with the prints fixed by the vapors of ethylacetate alone indicated that the azeotrope-fixed prints had less yellowing than the ethylacetate fixed prints.

What is claimed is:

1. The method of fixing a powder image containing a solvent soluble binder onto a backing web to which said powder image is loosely adhered, said method comprising the steps of exposing the web to a vapor atmosphere comprised of a constant boiling azeotropic mixture formed from .a two-phase mixture of water and a substantially Water-insoluble solvent for the binder for a time sufiicient to allow the azeotropic vapor to soften said powder to the point of adhesiveness whereby the softened powder image is caused to adhere to the surface of the backing web and then allowing the solvent to evaporate and leave a fixed image on said web.

2. The method of claim 1 wherein the organic solvent is a halogenated hydrocarbon.

3. The method of claim 1 wherein the organic solvent is trichloroethylene.

4. The method of claim 1 wherein the organic solvent is perchloroethylene.

5. The method of claim 1 wherein the organic solvent is an aromatic hydrocarbon.

6. The method of claim 1 wherein the organic solvent is benzene.

7. The method of claim 1 wherein the organic solvent is toluene.

8. The method of claim 1 wherein the organic solvent is an organic ester.

9. The method of claim 1 wherein the organic solvent is ethylacetate.

10. The method of claim 1 wherein the solvent soluble binder is polystyrene.

11. The method of claim 1 wherein the solvent soluble binder is isobutyl methacrylate.

5 12. The method of claim 1 wherein the solvent soluble binder is a polyamide.

13. The method of claim 1 wherein the solvent soluble binder is a rosin modified phenol formaldehyde resin.

References Cited 1 FREDERICK L. MATTESON, 111., Primary Examiner.

H. B. RAMEY, Assistant Examiner. 

